2.78 - switching between current shading mode and rendered one not work
There have been some recent changes in the default keymap for 2.78, Shift + Z now toggles between the current mode and Rendered mode, as opposed to before where it toggled always between SOLID and Rendered according to the release notes in the wiki.

Unfortunately Blender key map editor is not that good with merging changes between custom keymaps and changes to the official one.

My advice advice to you is to check out the new default keymap and manually copy the relevant operators like view3d.toggle_render and their corresponding key maps from there and paste it into your own custom key map with whatever new key binding you want, making sure you delete the old ones and eliminate any conflicts.